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European Journal of Echocardiography 2003 4(3):196-201; doi:10.1016/S1525-2167(02)00167-1
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Copyright © 2003, The European Society of Cardiology

Effects of postural changes on cardiac function in healthy subjects

B.P Paelinck1,*, J.W.M van Eck1, S.G De Hert2 and T.C Gillebert3

1Department of Cardiology, University of Antwerp, Belgium
2Department of Anesthesiology, University of Antwerp, Belgium
3Department of Cardiovascular Diseases, University of Ghent, Belgium

* Address correspondence to: Bernard P. Paelinck, Department of Cardiology, University Hospital Antwerp, Wilrijkstraat 10, 2650 Edegem, Belgium. Tel: +32 3 8214182; Fax: +32 3 8250848. bernard.paelinck{at}uza.be


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 References
 
Aims: To analyse the response of Doppler measurements to increased venous return in middle-aged healthy subjects.

Methods and Results: Left ventricular pulsed Doppler parameters, colour M-mode of early left ventricular filling and septal mitral annulus velocities were measured at baseline and after leg lifting (n=24). Leg lifting resulted in increased stroke volume (69 ± 14 to 74 ± 14 ml, P<0.01) and peak systolic annulus velocity (6.8 ± 1.3 to 7.3 ± 1.1 cm/s, P<0.01). Leg lifting enhanced peak early (E) mitral flow (74 ± 13 to 80 ± 14 cm/s, P<0.01), flow propagation (53 ± 10 to 59 ± 13 cm/s, P<0.01) and E' diastolic mitral annulus velocity (10.8 ± 2.2 to 11.7 ± 2.0 cm/s, P<0.01). There was a shortening of E wave deceleration time (178 ± 27 to 163 ± 27 ms, P<0.01) and isovolumic relaxation time (76 ± 11 to 68 ± 10 ms, P<0.01). However, individual changes in Doppler parameters differed among subjects.

Conclusions: Leg lifting improved myocardial function as manifested by increase in stroke volume, systolic annulus motion and acceleration of relaxation. Flow propagation velocity and diastolic mitral annulus velocities were influenced by the induced change in cardiac preload as well.

Keywords: load; ventricular function; Doppler; echocardiography


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 References
 
Doppler echocardiography has been widely used for evaluation of left ventricular haemodynamics[1]. However, the mitral inflow pattern is a dynamic phenomenon that depends not only on different degrees of elastic recoil, the rate and extent of myocardial relaxation and the chamber compliance, but also on the left atrial pressure[2]. The mitral inflow pattern, therefore, may rapidly change within the same patient, limiting to a crucial extent the prognostic value of a single baseline Doppler evaluation[3–6].

Loading manipulations[7,8] may induce dramatic variations in mitral inflow patterns, and the individual response may greatly vary between patients. The response with loading manipulations has been related to severity of cardiac disease[9] and preservation or deficiency of the length-dependent regulation of myocardial function (Frank–Starling's mechanism)[10,11].

Recently, analysis of colour M-mode Doppler images of early ventricular filling led to the concept of flow propagation velocity (Vp). Propagation velocity has been found to be mainly determined by left ventricular relaxation and closely related to {tau}. In contrast to the classical Doppler measurements, it has been reported to be relatively insensitive to altering loading conditions and is, thus, free of pseudonormalization[12–20].

Tissue Doppler imaging of the mitral annulus has been proposed as a new method for the evaluation of cardiac function. The velocity of the earliest diastolic motion (E') of the septal annulus reflects the rate of myocardial relaxation and correlates with {tau}. These velocities have also been shown to be less dependent on cardiac load as compared with the classical Doppler parameters. This implies that the ratio E/E' yields an important diagnostic value[21–23].

The response of Doppler indices to changing load in healthy hearts, however, remains poorly defined. The present study aimed to assess the effect of postural changes leading to increased venous return on Doppler indices in a healthy population.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 References
 
Subjects
Twenty-four healthy volunteers (20 men and four women, mean age 41 years, range 21 to 58) were studied. All subjects were referred for a medical check-up, which included complete cardiovascular questionnaire, clinical examination, electrocardiogram and routine echocardiogram.

Study protocol
The purpose of the study was explained to all the subjects, and informed consent was obtained. All investigations were performed at the University Hospital of Antwerp by two level III echocardiologists[24] (BPP, TCG).

An echocardiographic study was performed, including measurement of pulsed Doppler variables, colour M-mode of left ventricular filling and diastolic mitral annulus velocities. All measurements were repeated after 2 min stabilization following 45° leg lifting. Data were digitally stored for offline analysis.

Echocardiography
A Hewlett–Packard Agilent Sonos 5500 phased-array scanner (Andover, MA, USA) with 2.5-MHz transducer was used for Doppler recordings. Recordings were obtained during relaxed end-expiration, with the patient lying in supine left lateral decubitus. Transmitral flow was recorded in the standard apical four-chamber view, with the sample volume (size 1 to 2 mm) positioned between the tips of the mitral leaflets when E velocity was maximal and A contour sharp[25]. Consecutively, the sample volume (size 2 to 4 mm) was placed 1 to 2 cm into the right upper pulmonary vein to record pulmonary venous flow velocity. Left ventricular outflow tract velocity was measured from the apical long-axis view by placing the pulsed wave sample volume at the centre of the aortic annulus[2]. A colour M-mode Doppler image of left ventricular filling flow in early diastole was obtained from the apical four-chamber view, using the baseline-shifted first aliasing limit technique[16,17]. Mitral annulus velocities were measured by placing the sample volume in the apical four-chamber view at the septal side of the mitral annulus, taking extra care to have the annulus perpendicular to the direction of the emitted ultrasound waves[22,23,26].

Three consecutive cardiac cycles were acquired and stored for each parameter. Doppler echocardiograms were recorded at a sweep speed of 100 mm/s. All measurements were repeated after leg lifting.

Offline analysis was performed using the dedicated software of the ultrasound machine. For the transmitral flow, the peak velocity in early diastole (E wave) and at atrial contraction (A wave) was measured. The deceleration time of E wave was measured by extrapolating the initial slope of the E wave to baseline. The maximal velocities of pulmonary vein flow at systole (PVs), diastole (PVd) and atrial reversal (PVa) were measured. For determination of time velocity integral or stroke distance, the Doppler signal was traced. Stroke volume was determined by multiplying time velocity integral with cross-sectional area[27]. The velocity of flow propagation (Vp) was measured as the slope of the isovelocity contour of the first aliasing velocities from the mitral annulus in early diastole to typically 4 cm into the left ventricle[16,17]. From the tissue Doppler recordings, the following measurements were made: peak systolic velocity (Sa), early (E') and late (A') diastolic velocities.

Reproducibility
Blinded measurements were repeated by a second observer and by the first observer. Reproducibility was assessed as mean difference between two measurements and as mean percent error[21].

Statistical analysis
Group data are expressed as mean value ± SD. After testing for normality and equal variance, the two-tailed paired t-test was used to compare data before and after leg lifting. Relationships between changes of different parameters before and after leg lifting were described using linear regression analysis (SigmaStat 2.03 program). Statistical significance was set at P<0.01.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 References
 
In all subjects, recordings were considered satisfactory for analysis. As indicated in Table 1, there were no differences between heart beat interval and systolic and diastolic blood pressure before and after leg lifting.


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  		Table 1 Effects of leg lifting.

 
Data reproducibility
Analysis of peak E wave velocity showed a good intra- and inter-observer agreement, and the absolute difference was determined to be 1.8 ± 2.5 and 2.0 ± 2.5 cm/s and expressed as mean percent error of 2 ± 3 and 2 ± 3%, respectively.

Conventional Doppler measurements
After leg lifting, there were significant increases in E wave velocity (74 ± 13 to 80 ± 14 cm/s, P<0.01) and E wave deceleration slope (403 ± 129 to 457 ± 152 cm/s2, P<0.01). There were significant shortenings of deceleration time (178 ± 27 to 163 ± 27 ms, P<0.01) and isovolumic relaxation time (76 ± 11 to 68 ± 10 ms, P<0.01). A wave velocity remained unaltered after leg lifting (52 ± 10 to 55 ± 12 cm/s, P=ns), such as E/A ratio (1.44 ± 0.34 to 1.52 ± 0.34, P=ns), PVs (53 ± 8 to 56 ± 9 cm/s, P=ns), PVd (53 ± 10 to 52 ± 10 cm/s, P=ns) and PVa (29 ± 4 to 28 ± 3 cm/s, P=ns).

When individual changes in the response to leg lifting on E wave velocity (Figs. 1 and 2Go), E wave deceleration slope, E deceleration time, A wave velocity and pulmonary vein parameters were analysed, it appeared that the response was variable. In contrast, the response of isovolumic relaxation time to leg lifting was less variable, showing a shortening in most subjects (Figs. 3 and 4Go).


Figure 1
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  		Figure 1 Individual variability of the effect of leg lifting on mitral E wave velocity.

 


Figure 2
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  		Figure 2 Plot relating individual changes of stroke volume (SV) (ml) and E wave velocity (E) (cm/s). No correlation was found between both parameters.

 


Figure 3
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  		Figure 3 Plot relating individual changes of Vp (cm/s) and isovolumic relaxation time (IVRT) (ms). No correlation was found between these two parameters of early diastole.

 


Figure 4
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  		Figure 4 Plot relating individual changes of isovolumic relaxation time (IVRT) (ms) and stroke volume (SV) (ml). No correlation was found between both parameters.

 
Flow propagation and diastolic mitral annular velocities
There was a significant increase in Vp (53 ± 10 to 59 ± 13 cm/s, P<0.01), E' (10.8 ± 2.2 to 11.7 ± 2.0 cm/s, P<0.01) and A' (9.7 ± 1.8 to 10.7 ± 1.9 cm/s, P<0.01). E/E' (7 ± 1.6 to 7.1 ± 1.9, P=ns) and E/Vp (1.43 ± 0.37 to 1.41 ± 0.37, P=ns) did not change. Again, the individual response to leg lifting of mitral annulus velocities varied among subjects (Fig. 5). In contrast, Vp showed an increase in most subjects, except for minimal decrease in some (Figs. 3 and 6Go). No correlation was found between individual changes of diastolic parameters ({Delta}Vp = 6.363 + (0.0391 x {Delta} isovolumic relaxation time), r=0.0479, P=0.824).


Figure 5
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  		Figure 5 Plot relating individual changes of diastolic E' and systolic Sa. No correlation was found.

 


Figure 6
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  		Figure 6 Plot relating individual changes of Vp (cm/s) and stroke volume (SV) (ml). No clear correlation was found between both parameters.

 
Systolic indices
With leg lifting, there was a significant increase in time velocity integral (22.2 ± 4.3 to 23.4 ± 4.3 cm, P<0.01), stroke volume (69 ± 14 to 74 ± 14 ml, P<0.01), cardiac output (4.48 ± 0.89 to 4.87 ± 1.21 l/min, P<0.01), left ventricular ejection time (286 ± 20 to 293 ± 18 ms, P<0.01) and Sa (68 ± 1.3 to 7.3 ± 1.1 cm/s, P<0.01).

While the individual response to leg lifting was variable for Sa between subjects (Fig. 5), stroke volume increased in all subjects except in some, where no measurable changes were observed (Figs. 2, 4 and 6GoGo).

Systolic and diastolic indices
No relationship between systolic and diastolic changes was found. No correlation was observed between individual changes in stroke volume and changes in E wave velocity ({Delta}stroke volume = 3.714 – (0.0247 x {Delta}E), r=0.0634, P=0.769) (Fig. 2), changes in isovolumic relaxation time ({Delta} isovolumic relaxation-time = –9.924 + (0.566 x Delta; stroke volume) (Fig. 4), r=0.256, P=0.227) and changes in Vp ({Delta} Vp = 3.890 + (0.663 x {Delta} stroke volume), r=0.368, P=0.077) (Fig. 6). The same observation was made for changes in systolic and diastolic annulus velocities ({Delta}E'=1.038–(0.146x{Delta}Sa), r=0.0725, P=0.736) (Fig. 5).


   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
References
 
Leg lifting induced an increase in venous return. Through length-dependent activation of myocardial function (Frank–Starling's law), the resulting volume loading induced a mild augmentation of systolic function. Increased myocardial contractility was apparent from a significant augmentation of stroke volume and an increased systolic mitral annulus velocity, which reflected longitudinal shortening of the left ventricular chamber and left ventricular ejection rate[28,29]. Similar effects and improved ventricular function were seen in open chest open pericardium coronary surgery patients. In addition, in these patients, a tight coupling between contraction and relaxation could be demonstrated[30].

Parallel with the effects on systolic function, changes appeared in diastolic Doppler parameters. Together with a shortening of isovolumic relaxation time, the mitral filling pattern showed an increased E wave deceleration along with a shortening of deceleration time. These Doppler changes may either result from the development of elevated filling pressures or from accelerated relaxation occurring as a consequence of increased contractility. Since both E/E' and E/Vp remained unchanged, increased pulmonary capillary wedge pressures and hence left ventricular filling pressures were unlikely[19,31,32]. Since the present study was performed in healthy subjects, free from cardiac disease, the observed Doppler changes are likely to result from an acceleration of relaxation. Such an improved left ventricular systolic function and accelerated relaxation in response to increase in cardiac load have also been shown in other study designs in patients with preserved cardiac contractile reserve[10,33,34]. Shimizu et al. described the effects of leg lifting in a combined groups of normal subjects, patients with hypertensive heart disease and dilated cardiomyopathy. Although they could not make inference on the normal response to this intervention, the present study confirmed their data[35].

An intriguing observation of the current study was that in contrast to previous studies[31,36], the diastolic septal tissue Doppler parameters and Vp also seemed to be affected by increased venous return induced by leg lifting. There was an increase in E' and A' and an acceleration of Vp. The present study did not allow comment on the possible underlying mechanisms for this observation. However, the current results suggest a potential limitation of most diastolic Doppler parameters in the evaluation of filling haemodynamics. Not only mitral flow parameters but also mitral annulus velocities and Vp displayed variable responses to the increase in cardiac loading conditions. This indicated that newer Doppler-derived indices of diastolic function (Vp and E') appear to be altered by changes in loading conditions as well, induced by a single postural change. No relationship was found between individual changes in different diastolic and systolic parameters (Figs. 2, 4, 5 and 6GoGoGo). Individual changes in E wave velocity, isovolumic relaxation time and Vp did not show any correlation with changes in stroke volume. The same applied for changes in systolic and diastolic annulus velocities. Because only minor quantitative changes between different parameters were seen in a small cohort of subjects, the study lacked statistical power to show this correlation. Consequently, the study points to the variability of the answer of Doppler indices in healthy subjects causing inability to predict the individual answer of healthy hearts to increased cardiac load.

We sought to assess an unselected group of healthy subjects who would be representative of a broader population. Selection bias, however, could have influenced these results. A broader study group could overcome these problems and add statistical power. In addition, a study sample with equal distribution of subjects of each gender would have been more representative of a broader population. A standardized leg-lifting manoeuvre was used. In previous studies, we demonstrated that leg elevation induced a predictable and uniform increase in end-diastolic volume, hence preload[30]. Further studies using additional invasive methodology are necessary to elucidate whether the response on Doppler indices due to an increase in cardiac load may depend on the relative load at which the ventricle is actually working. Relative load is evaluated by operating pressure divided by peak isovolumic pressure[37].

In conclusion, in healthy subjects, leg lifting enhanced systolic function (Frank–Starling's law). The changes in the transmitral flow pattern reflected accelerated relaxation. However, the responses on measures of diastolic function are variable, and the individual change of Doppler parameters in response to increased cardiac load could not be predicted. In contrast to previous reports, the velocity of flow propagation and diastolic mitral annular velocities also appear to be influenced by an alteration in cardiac load.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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